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14 November 2014

Hybrid sapsucker?

You can imagine my chagrin in discussing hybrids just a couple of days after mentioning that most birders reel back in fear when you mention the "H word". Good thing I quietly reside outside of the circle of most birders.

So here's the deal... I was birding at a local patch here in Sacramento County (Garcia Bend Park: 38.482632, -121.546743) when I found an interesting sapsucker. I didn't get great looks or great photos; here are the only 5 in existence:

Luckily, because it's likely obvious to those who a) know sapsuckers or b) are willing to open a bird book, this clearly isn't a Williamson's or Red-breasted sapsucker. So, yay, we're making progress! In fact, I'm 100% positive that this bird is one of the following options:

1) a pure RED-NAPED SAPSUCKER

2) a pure YELLOW-BELLIED SAPSUCKER

3) a hybrid between those two species

That leaves us with one question ("What is this thing?!) that stems into a lot of questions ("Why is it that thing?"). You see, I discovered pretty quickly that this bird isn't very straightforward. I mean, it lacks a red nape but has some red feathers in the lower throat. Hmm! So now the deliberation begins.

Before we go much further, there are a couple of other potentially important things we need to figure out. Mainly, what sex is this bird and could it be a youngster?

Age: I've done some reading on this issue and discussed this bird with several people now. One thing that came out of these discussions is that this is an adult bird. I've heard from multiple sources that the black shield on the breast isn't shown on first-year birds until spring, even for RN. And it's certainly not a young YB; they don't finish their molt until much later. So, if you're willing to believe that, we're dealing with an adult!

Sex: So knowing the age really helps us determine the sex. Very simplistically, adults males of both RN and YB always show completely red throats. So there you go, we're dealing with an adult female.

Nape: Many of the books I have say nebular things like "Red-naped doesn't always have a red nape". That gave me pause before reading Mlodinow et al. (2006). That article discusses how this point is essentially due only to wear and that it's most likely to occur in the summer months. They conclude that any sapsucker without a red nuchal patch between 1 October and 1 May is almost certainly not a RN. Although this picture doesn't show the best angle, I think it's enough to suggest that this bird doesn't have red on the nape:

So with our bird, that's a likely strike against a pure RN.

Throat: One of the things that makes this mystery bird so interesting are the few red feathers on the lower throat, visible here:

I had always been under the impression that a pure YB never showed any red in the throat. Now I know that's incorrect! Mlodinow et al. (2006) stated that up to 7% of female YB have varying amounts of red in the throat (they even have a cool photo of one in the article that matches our mystery bird quite well). They also include photos of a hybrid female and state in the caption that "the white throat with red corners is not uncommon among hybrid females". Thus, it's safe to say that our mystery bird has the throat pattern of either a rare YB or hybrid.

Supercilium: A fieldmark that I hadn't focused on until recently is the thickness of the supercilium; roughly speaking, RN have thinner white superciliums compared to YB. Mlodinow et al. (2006) discuss this fieldmark in their article and conclude that, although there is probably overlap, the subtle feature can be helpful. In looking online at lots of pictures, I agree that it's quite noticeable. It's my opinion that our mystery bird shows this relatively thin supercilium that doesn't flare out towards the rear and thus favors RN.

Malar: Although less helpful (at least I think so), the relative thickness of the white malar stripe can also be used as a supporting fieldmark. Generally speaking, RN have thinner white malars than YB. Like with the supercilium, I think our mystery bird fits well with RN on this trait.

So maybe it's time to summarize some things about our mystery bird...

Marks that favor RED-NAPED:

Narrow supercilium

Narrow while malar stripe

Marks that favor YELLOW-BELLIED:

Lack of red on the nuchal patch

Throat pattern (although only rarely; this also favors a hybrid)

Clearly I think it's time we should consider the third option; a hybrid. Mlodinow et al. (2006) discusses how these species are only known to hybridize in a limited part of southwestern Alberta. Although they were said to interbreed freely there, it's estimated that only about 5,000 of these hybrids exist. In other words, they're hella rare. However, it's also stated that their wintering range isn't known. "Hmmmm" said the Central Valley birder.

I should add a caveat; I wasn't able to see the pattern on the back of this bird which could be another helpful trait to study. Similarly, if someone were able to take better photos of the nape, that could also be helpful. In fact, those photos could turn this silly analysis on its head.

But seriously, does this bird fit the model of hybrid? I believe the above conflicting identification points are enough to call this a hybrid. We have fairly reliable traits pointing to two different species. Is it possible that this could be a pure RN or YB? Well, I suppose so but I personally don't see that as likely.

If you want to read more, I highly recommend this article that was published in Birding in 2006. It goes way more in-depth than I do!